To assess the relationship between left ventricular (LV) volume overload and LV systolic functIon in chronic aortic regurgitation (AR), 80 patients were studied by both echocardiography at rest and radionuclide cineangiography at rest and during exercise. LV fractional shortening remained within the normal range until LV diastolic dimension by echo exceeded 65 mm and LV systolic dimension exceeded 42 mm (both representing a 40% increase above expected normal values). Above these dimensions, systolic dimension increased disproportionately greater than diastolic dimension, and fractional shortening fell progressively. Similarly radionuclide cineangiographic LV ejection fraction (EF) at rest and during exercise and normal in patients with LV dimensions increased up to 40% above normal. Above this value, EF was often normal at rest, but was subnormal in 96% of patients. Thus, the LV can increase its internal dimensions approximately 40% and maintain normal systolic function. Above this point further dilation is accompanied by a progressive LV systolic dysfunction.